The invention pertains to a steering angle sensor for determining the absolute angular position of the steering wheel of a motor vehicle, with a first sensor unit consisting of a sensor that carries a first coding and is coupled to the rotational movement of the steering wheel as well as a detection device that is arranged on the side of the stator and serves for scanning the coding of the sensor within an angular segment of the entire range of rotation of the steering wheel, and with a second sensor unit consisting of a rotor that is coupled to the sensor of the first sensor unit via corresponding gears, a coding that can be moved by the rotor and a detection device that is arranged on the side of the stator and serves for scanning this coding within the entire range of rotation of the steering wheel.
The steering angle or the steering angle deflection in motor vehicles is, for example, required in driving dynamics control systems. Such a driving dynamics control system receives other measuring data in addition to the aforementioned steering angle values, e.g., the rotational speed of the wheels or the turning of the motor vehicle about its vertical axis. In this case, the absolute steering angle deflection as well as the steering speed are required for evaluating these values by the driving dynamics control system together with the other measured data, with said data subsequently being used for controlling actuators, e.g., the brakes and/or the engine management system.
A steering angle sensor of the initially mentioned type is known from DE 44 09 892 A1. The first sensor unit of this steering angle sensor, the sensor of which is directly coupled to the rotational movement of the steering wheel in the form of a rotor, carries out an angular measurement within one revolution of the steering wheel (360xc2x0), i.e, within an angular segment of the entire range of rotation of the steering wheel which amounts to four revolutions of the steering wheel (1440xc2x0) for the object of this document. The second sensor unit serves for counting the revolutions so as to provide information as to the fact within which revolution of the entire range of revolution of the steering wheel the current angular position measured with the first sensor unit is located. This is the reason why the rotor of the second sensor unit is designed for measuring the entire range of rotation of the steering wheel which amounts to 1440xc2x0 within 360xc2x0. For this purpose, the rotor of the second sensor unit is driven by the rotor of the first sensor unit similar to a planetary gear with a step-down ratio of 4:1. The axes of rotation of the two rotors are arranged concentric to one another such that the rotors of both sensor units are arranged in one plane. The inner rotor is connected to the steering spindle such that both parts rotate together, i.e., this rotor drives the outer rotor of the second sensor unit via the planetary gear when the steering wheel is turned.
In order to realize this step-down gear in the described fashion, the planetary wheel used needs to have certain dimensions. The concentric arrangement between the steering spindle, the rotor of the first sensor unit and the rotor of the second sensor unit as well as the arrangement of the planet wheel cause this steering angle sensor to circumferentially require a significant installation space in the radial direction referred to the steering axis. Consequently, it is not always easily possible to arrange this steering angle sensor in a steering column module; this also applies to the arrangement of the steering angle sensor in a lower region of the steering spindle, e.g., above the pedals.
The sensor units of this known steering angle sensor utilize a magnetic coding similar to a Gray code as the coding and Hall sensors which are circumferentially arranged on the side of the stator, i.e., distributed over 360xc2x0, as the detection devices that scan the magnetic coding. Each sensor unit contains such a Hall sensor arrangement.
Based on this state of the art, the present invention aims to propose a steering angle sensor of the initially mentioned type which is not only optimized with respect to the required installation dimensions, but can also be realized with a lower expenditure of hardware without having to accept disadvantages regarding the functionality of the steering angle sensor.
According to the invention, this objective is attained due to the fact that the detection device of the first sensor unit is realized in the form of a sensor array with a series of converter elements that adjoin one another, and due to the fact that this sensor array is arranged such that the coding of the sensor of the first sensor unit as well as the coding of the second sensor unit can be scanned, with the sensor of the first sensor unit being realized in the form of a code disk, with the sensor array being arranged such that its longitudinal extent lies transverse to the moving direction of the coding of the code disk and its converter elements point to the flat side of the code disk which carries the coding, and with a differential planetary gear being provided for realizing the coupling of the rotor of the second sensor unit to the sensor of the first sensor unit, wherein the planetary gear contains a driving wheel that is realized in the form of a translating gear wheel and meshes with the sensor of the first sensor unit as well as a stationarily arranged reference wheel of annular design which contains an internal gearing and is arranged adjacent to the driving wheel, wherein a planet wheel that is engaged with the internal wheel gearing as well as the rotor of the second sensor unit which is realized in the form of the driven wheel of the gear and contains a different number of cogs than the reference wheel is arranged between a pinion that is situated on the hub of the driving wheel and the internal gearing of the reference wheel, and wherein the rotor engages with a pivoted lever into a claw of an arm that carries the coding of the second sensor unit and is arranged in a pivoted fashion between the code disk that is realized in the form of a sensor and the sensor array.
The steering angle sensor according to the invention contains two sensor units, with the different codings of both sensor units acting upon a common detection device. For this purpose, the detection device of the first sensor unit is realized in the form of a one-dimensional or two-dimensional coherent sensor array with a series of adjoining converter elements. The two sensor units preferably operate in an optoelectronic fashion, with the coding of the first sensor unit being formed by a code disk that is illuminated from one side, and with the sensor array that, for example, is realized in the form of a line sensor being arranged on the side of the code disk which is situated opposite to the light source such that its photosensitive surface points to the code disk.
The sensor which carries the coding of the first sensor unit may, for example, consist of a rotor that is directly coupled to the rotational movement of the steering spindle, e.g., a circular code disk or a sensor element that is translationally moved referred to the rotational movement. In the latter instance, the sensor element is coupled to the rotational movement of the steering spindle by means of a gear coupling, e.g., a gear train. If the sensor is realized in the form of a code disk, the coding of this code disk may, for example, contain an Archimedean spiral that is realized in the form of a light slot, with a circular reference track that is arranged centrally referred to the code track being assigned to the code track in order to increase the measuring accuracy. This reference track may be realized in the form of a light slot analogous to the code track or consist of the circumferential edge of the code disk. Instead of utilizing light slots, the tracksxe2x80x94code track and reference trackxe2x80x94may also be realized in the form of black tracks that stand in contrast to an otherwise transparent code disk.
In the step-down gear, the rotor of the second sensor unit is coupled to the sensor of the first sensor unit which, in turn, is coupled to the movement of the steering wheel. The rotor of the second sensor unit contains a pivoted lever that engages into a claw of an arm that carries the coding of the second sensor unit and is arranged in a pivoted fashion between the code disk that forms the sensor and the sensor array. In this case, a movement of the driven rotor results in a pivoting movement of the arm, the coding of which acts upon different regions of the sensor array within the entire range of rotation of the steering wheel, namely in accordance with the angular position of the steering wheel. The maximum travel of the arm of the second sensor unit may correspond to no more than the longitudinal extent of, for example, a line sensor used. Since the movement of the driven rotor can only amount to a short distance for this reason, the step-down ratio between the sensor of the first sensor unit and the rotor of the second sensor unit needs to be correspondingly high. For this purpose, one utilizes a differential planetary gear that contains a driving wheel which is realized in the form of a translating gear wheel and meshes with the sensor of the first sensor unit that, for example, is realized in the form of a rotor as well as a reference wheel. The reference wheel has an annular design, contains an internal gearing and is arranged on the side of the frame. A pinion that is coupled to the movement of the driving wheel via a planet wheel situated between the pinion and the reference wheel is arranged on the hub of the driving wheel. The rotor of the second sensor unit represents the driven wheel of this gear arrangement and is driven by the planet wheel, with the number of cogs of the driven rotor differing from that of the reference wheel. When designing such a planetary gear, it is practical for space reasons to arrange the driving wheel and the driven wheel inside one another, with the reference wheel that contains the internal gearing being stationarily arranged concentric to and within the driving wheel, and with the internal gearing of the reference wheel surrounding the driven rotor.
The use of only one detection device for both sensor units causes the number of required detection devices to be reduced in comparison to the state of the art. The arrangement of the gear coupling in the described fashion, in which the two rotors are, in contrast to the state of the art, not arranged concentric to one another, but rather adjacent to one another, means that a greater installation depth than the radial installation depth of the first sensor unit is only required radially of the rotational axis of the first sensor unit in one region, namely in the region in which the planetary gear is arranged. Only the installation depth defined by the first sensor unit is required in the remaining sections of the steering angle sensor.